It has become the abiding image of the Josef Fritzl trial: the blue ringbinder folder the accused has used to hide his face from the cameras when he enters court.

Under Austrian law, defendants are permitted to take their own legal documents into the courtroom, and the blue ringbinder, made by office supply manufacturer Esselte, contains his personal legal papers.

Erich Huber-Günsthofer, the deputy head of the prison where Fritzl has been held since his arrest last April, has stressed that the folder was not provided by the courts as a prop, and Fritzl was legally entitled to carry it in whatever way he felt fit.

Close-up shots of papers contained within the folder show what appears to be a compensation claim from one of his daughters, Monika, who was born in the cellar in 1994. According to media reports, it referred to the cost of her mental health treatment — €63,672 (£59,000).

After the first day of the trial, Fritzl's lawyer Rudolf Mayer explained why his client used the ringbinder. "He was simply embarrassed," he said.